One of the tools used for side machining of a scroll built in a scroll compressor is an end mill. FIG. 25 shows an end mill 100 used for side machining of the scroll (spiral vane). In FIG. 25, 102 denotes a cutting edge, 103 denotes a groove between the cutting edges 102, 104 denotes a core diameter, 105 denotes a shank serving as a portion which holds the end mill 100 with a jig or the like, and 106 denotes an angle of torsion of the cutting edge. FIG. 26 shows a scroll 107, being a workpiece to be machined, and the scroll 107 has a scroll tooth 108.
When side machining of the scroll tooth 108 of the scroll 107 is to be carried out by the end mill 100, the shank 105 of the end mill 100 is fitted to a rotation unit such as a motor, to rotate the end mill 100 by the rotation unit. At this time, the scroll 107 or the end mill 100 is shifted so as to follow the scroll shape, while the cutting edge 102 of the end mill 100 is brought into contact with the side face of the scroll tooth 108, thereby side machining of the scroll tooth 108 is carried out.
In the side machining by the end mill 100, however, the position where the cutting edge 102 contacts with the machined surface of the scroll tooth 108 changes due to the torsion of the cutting edge 102. Particularly, as the angle of torsion 106 decreases, the change of the contact position of the cutting edge 102 increases. As described above, in the side machining by the end mill 100, since the distance between the position where the shank 105 is fitted and the position where the cutting edge is brought into contact with the scroll tooth changes largely, the machining load varies largely, causing a problem in that high machining accuracy cannot be ensured. With a small-diameter end mill 100 having a large groove 103 and a small core diameter 104, the rigidity becomes low, and the end mill 100 bends, causing a problem in that the machining accuracy decreases.
Therefore, for this kind of machining, a grinder is often used. An ordinary grinder in which a binder is formed of vitrified or resin, is formed by mixing and stirring abrasive grains and the binder powder, followed by molding into a desired shape, and sintering the molded article. Therefore, minute holes exist therein, and hence the chips discharging property is not so bad. On the other hand, an electrodeposited grinder is produced by holding the abrasive grains by plating, and hence minute holes existing in the ordinary grinder do not exist, thereby deteriorating the chips discharging property.
FIG. 27 shows a columnar electrodeposited grinder 109 used for side machining of the scroll. In FIG. 27, 110 denotes a columnar base metal, 111 denotes a plating layer formed of nickel or chromium on the side face of the base metal 110, and 112 denotes abrasive grains of CBN or diamond arranged in one layer on the surface of the plating layer 111, and the abrasive grains 112 are put together at random and fixed on the plating layer 111.
When side machining of the scroll tooth 108 of the scroll 107 is to be carried out, using such an electrodeposited grinder 109, a portion of the grinder base metal 110 of the electrodeposited grinder 109 where the abrasive grains 112 are not electrodeposited is fitted to a rotation unit such as a motor, and the electrodeposited grinder 109 is rotated by the rotation unit. At this time, the electrodeposited grinder 109 or the scroll 107 is shifted so as to follow the scroll shape, while the abrasive grains 112, being the cutting edge, are brought into contact with the side face of the scroll tooth 108, thereby side machining of the scroll tooth 108 is carried out.
In the above electrodeposited grinder 109 in the conventional art, since the abrasive grains 112 are put together at random and fixed on the whole surface of the grinder, lots of abrasive grains as the cutting edge work on the machined surface, regardless of the existence of truing, thereby causing a problem in that the machining load is large. Particularly, since a small-diameter grinder has small shaft rigidity, it easily deforms, and has a problem in that the grinder bends to decrease the machining accuracy, or the grinder life is shortened, due to an increase of the machining load.
As described above, in the conventional electrodeposited grinder, since the abrasive grains are put together at random on the whole surface of the grinder, lots of abrasive grains as the cutting edge work on the machined surface, to increase the machining load, thereby it is difficult to obtain high machining accuracy. The conventional electrodeposited grinder has also poor chips discharging property.
In JISB4130 and JISB4131 in the JIS Standard, there is an indication relating to the grain size of abrasive grains of the CBN or diamond electrodeposited grinder, and the shape of the grinder. This indication, however, relates to the grain size of the abrasive grains 112 and the shape of the grinder base metal 110, and does not indicate the arrangement of the abrasive grains 112 on the surface of the grinder base metal 110.
Techniques relating to the truing method and the dressing method of the grinder are shown in JISB4134, JISB4135, JISB4136 or JISB4137 in the JIS Standard. These are for installing tools for truing or dressing so as to come in contact with the grinder to carry out truing and dressing.
These conventional art shown in the JIS Standard is a method for bringing the tool into contact with the grinder, and hence machining resistance is produced at the time of truing or dressing, causing unintended exhaustion of the cutting edge, dropout of abrasive grains or exhaustion of the binder, and further there is a problem of short life span of the tool. Further, there is a disadvantage in that deformation or cracking may occur with respect to a grinder with a small-diameter shaft having low rigidity, a grinder with a thin blade, or a small-diameter end mill.
Therefore, there has been proposed a technique for performing non-contact truing or dressing, using a laser beam. The technique relating to the non-contact truing or dressing is disclosed in, for example, Japanese Patent Application Laid-Open No. 11-285971 shown in FIG. 28.
In this conventional art, at either a time of stopping or rotating a grinder 113, a laser beam is irradiated from a laser oscillator 115 to a grinder use plane 114a or a grinder auxiliary use plane 114b through a lens 116, to dissolve and evaporate a binder, to thereby adjust the amount of abrasive grains to be protruded and the outline of the abrasive grains. The grinder use plane 114a or the grinder auxiliary use plane 114b is observed by a portable confocal laser microscope 117. A feedback mechanism 118 determines the optimum conditions of the maximum laser output and pulse width to obtain a desired amount to be protruded and the optimum conditions of the laser irradiation position to obtain a desired grinder outline, and feeds back the determined optimum conditions to the laser oscillator 115.
In the conventional non-contact dressing and truing methods, it is disclosed that only the binder on the use plane of the grinder or on the auxiliary use plane of the grinder is dissolved and evaporated without damaging the abrasive grains, by using a laser beam having a wavelength other than the wavelength at which absorption of infrared rays and ultraviolet rays and selective absorption of impurities take place, to thereby control the amount of abrasive grains to be protruded and the grinder outline. However, control of a difference ingrain size of the abrasive grains and a difference in height of working abrasive grains of the grinder is not disclosed therein.